net: Inline skb_pull() in eth_type_trans().

In commit 6be8ac2f ("[NET]: uninline skb_pull, de-bloats a lot")
we uninlined skb_pull.

But in some critical paths it makes sense to inline this thing
and it helps performance significantly.

Create an skb_pull_inline() so that we can do this in a way that
serves also as annotation.

Based upon a patch by Eric Dumazet.

Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/skbuff.h

@@ -1128,6 +1128,11 @@ static inline unsigned char *__skb_pull(struct sk_buff *skb, unsigned int len)
 	return skb->data += len;
 }
 
+static inline unsigned char *skb_pull_inline(struct sk_buff *skb, unsigned int len)
+{
+	return unlikely(len > skb->len) ? NULL : __skb_pull(skb, len);
+}
+
 extern unsigned char *__pskb_pull_tail(struct sk_buff *skb, int delta);
 
 static inline unsigned char *__pskb_pull(struct sk_buff *skb, unsigned int len)

net/core/skbuff.c

@@ -1051,7 +1051,7 @@ EXPORT_SYMBOL(skb_push);
  */
 unsigned char *skb_pull(struct sk_buff *skb, unsigned int len)
 {
-	return unlikely(len > skb->len) ? NULL : __skb_pull(skb, len);
+	return skb_pull_inline(skb, len);
 }
 EXPORT_SYMBOL(skb_pull);
 

net/ethernet/eth.c

@@ -162,7 +162,7 @@ __be16 eth_type_trans(struct sk_buff *skb, struct net_device *dev)
 
 	skb->dev = dev;
 	skb_reset_mac_header(skb);
-	skb_pull(skb, ETH_HLEN);
+	skb_pull_inline(skb, ETH_HLEN);
 	eth = eth_hdr(skb);
 
 	if (unlikely(is_multicast_ether_addr(eth->h_dest))) {